Objectives of the kind mentioned at the outset are normally composed of many different components such as lenses, mounts, housings and control elements, which, in the following text, are subsumed under the term “objective elements”. A common stipulation during the development of an objective is that one or more components in the interior of the objective, for example an optical system, be protected to the best possible extent, from external influences such as spray or dust. To this end, provision is often made for seals or sealing systems between the individual objective elements. It is comparatively easy to seal objective elements which are arranged immobile relative to one another by means of a multiplicity of known sealing techniques. It is difficult to seal moveable objective elements in a durable and reliable fashion.
U.S. Pat. No. 4,440,403 discusses this problem and discloses a waterproof and dust-proof seal for a rotatable operating element of a camera. The housing of the camera has an annular projection over which the rotatable operating element is arranged. The seal comprises an intermediate ring, which is placed in rotatable fashion on the annular projection, and a flexible sealing ring, which forms the connection between the intermediate ring and the operating element. The inventive concept can also be applied to an objective tube.
U.S. Pat. No. 4,168,897 furthermore discloses a focus adapter for an underwater camera, which is connected to the camera with a seal.